This invention relates to a working tool with a replaceable working bit, and also to the replaceable working bit per se.
The invention is concerned generally with a working tool, which necessarily is provided with one or more working edge or face which is designed to work on a particular material, and which therefore is exposed to wearing action over a period of time.
However, the invention has been developed primarily in connection with a working tool which is capable of working on soil or similar material e.g. sand, gravel, stone, rubble, and which usually has a working edge to engage the working material concerned. The working edge will be subject to wear over a greater or lesser period of time, depending upon the required operation, and the material being handled.
In some blade-type of working tools, it is acceptable to carry out sharpening of the edge as it becomes worm, and this can be done a number of times (by progressive erosion into the main body of the tool) but eventually the entire tool has to be scrapped. In other working tools, it is known to provide replaceable working edges, which are secured to the main body of the tool by threaded fasteners e.g. bolts or screws, and which are sacrificial, in the sense that the working edges protect the main body of the tool from wear (which is the expensive component), and which are replaced when an unacceptable level of wear has occurred in the replaceable part.
In connection with soil working tools for use in agriculture, there are many examples of working elements or working xe2x80x9cbitsxe2x80x9d which are replaceably mounted on the main body of the tool concerned e.g. a xe2x80x9cpointxe2x80x9d on the share of a plough, a knife on a plough body, or a tip of a cultivator tine.
In all of these arrangements, it is usual to mount the working element in position by means of two separate threaded fasteners. This gives a robust mounting of the elements, and by reason of using two separate fasteners, the element is well able to resist any twisting or turning moments which may be applied to the element in service, in addition to providing shear resistance to any direct forces tending to separate the element from the tool.
Evidently, when it become necessary to replace a worn element, the two fasteners have to be released, and a replacement element then installed in place. If this is carried out xe2x80x9cin the fieldxe2x80x9d, this is a time consuming and difficult task, especially, as is often the case, the fasteners or nut fixings have become damaged, rusted or otherwise become difficult to release. The same will apply in respect of routine maintenance carried out prior to use. In extreme cases, it is necessary to use a cutting torch to release the fasteners.
Bearing in mind that a large cultivator might have up to sixty separate cultivator tines (each with its own replaceable tip), it can be a major operation to replace a full set of worn tips.
In extreme soil conditions e.g. heavy clay plus flints, a new set of cultivator tips can become worn within three hours and then need replacement. A tractor to propel such large cultivators might cost of the order of £200,000 (about $315,000), and is therefore an extremely expensive piece of capital equipment, and possible xe2x80x9cdowntimexe2x80x9d of the order of three hours represents a serious under utilisation of such a high capital cost item.
With a view to simplify the assembly and dis-assembly of replaceable wearing parts, it is known to provide a mounting arrangement on the main body of the tool which only requires a single fastener, but necessarily this requires the provision of a suitably shaped seating which holds the wearing part captive against rotation about the axis of the single fastener.
One example of such a known mounting arrangement comprises an assembly of a replaceable wearing part on a main body of a cultivator tine, in which the wearing part has a rectangular body which merges into a V-shaped tip at one end, and on its opposite end it has a narrow projecting lug. A single fastener is taken through the body and through a mounting hole in the tine, and a shaped socket or receiving recess also in the tine receives the projecting lug in order to provide resistance to any turning action which may be applied in service to the tip and tending to rotate the tip about the axis of the fastener.
In this known arrangement of replaceable cultivator tip, there is still the disadvantage of assembly and dis-assembly of the fastener, but in addition the projecting lug only forms a narrow prolongation of the main body of the tip i.e. the main-body is much wider than the lug, and the lug is therefore the sole means of resisting turning forces applied to the tip about the axis of the fastener. Therefore, this construction relies for its strength on the narrow lug, and on which highly concentrated stresses may be generated in service which may result in premature failure.
The invention therefore seeks to provide a novel arrangement of replaceable wear part or bit for mounting on a leading edge of a working tool, and which can be mounted in a working position on the tool, and be secured against displacement from the working position, without need for threaded or other separate removable fastener(s).
According to one aspect of the invention there is provided a replaceable wear part for mounting on a leading edge of a working tool, said leading edge and said wear part having co-operative guide formations extending generally perpendicular to the leading edge and which provide a socket and projection type of slidable interfit whereby the wear part can be driven by a force extending generally perpendicular to the leading edge in order to take-up a working position in which it is secured against displacement from the working position by frictional interengagement between the guide formations on the wear part and the leading edge, and without need for threaded or other separate removable fastener.
Therefore, a replaceable wear part according to the invention can be driven e.g. by a hammer to take-up its working position, and the co-operative guide formations allow the wear part to slide in a direction generally perpendicular to the leading edge. The guide formations are arranged to exert a wedging action on the wear part, so that the greater the distance travelled, the stronger will be the frictional engagement forces acting between the guide formations.
In a preferred arrangement, the guide formations in the leading edge of the tool form a socket whose width reduces with distance perpendicularly inwardly of the leading edge, so that a progressively increasing wedging force can act on a wear part as it is driven internally of the socket.
The socket may be defined between a pair of opposed side walls which are convergent or taper, and the wear part has opposed external side faces which are also convergent or taper, but to a greater extent than the tapering of the side walls of the socket, so that an increasing wedging force is generated therebetween as the wear part is driven to its working position, whereby also the frictional resistance against possible displacement increases progressively.
The co-operative guide formations preferably also have an interengagement which opposes any relative rotation of the wear part about its longitudinal axis.
The walls or faces defining the guide formations may be of matching V-shape in cross section, though other cross sectional shapes may be provided, such as to oppose rotation of the wear part about its longitudinal axis, and relative to the leading edge.
Preferably, the invention comprises an assembly of the replaceable wear part and the working tool in combination.
The wear part may comprise a working bit to be mounted on a transversely extending leading edge of an agricultural tool, such as a xe2x80x9cpointxe2x80x9d (preferably a reversible point), a ploughshare, or a cultivator tine. However, the invention may be applied to other types of working tool than agricultural tools e.g. an excavator bucket (front or rear mounted), or a loading shovel, each having a leading edge provided with excavator teeth mounted thereon along the length of the leading edge, in which each excavator tooth comprises a replaceable wear part according to the invention.